Electrically Tunable Second Harmonic Generation in the Lu₂O₃ Plasmonic Tunnel Junction

Nanostructures utilizing noble metals have been widely used to realize localized surface plasmon resonance (LSPR) for several decades. Their unique optical properties, especially strong near-field enhancement, provide a platform for strong light-matter interaction such as for nonlinear light generation, surface-enhanced Raman scattering (SERS), and plasmon-exciton coupling. Tunnel junctions, typically composed of sub-nanometer scale (<5 nm) insulating layer and metal electrodes, can be engineered to support LSPRs. With tunable electrical and optical response, plasmonic tunnel junctions can be leveraged to electrically control light-matter interaction in ultrathin insulating gaps. Here, we observe electrically tunable second harmonic generations (SHG) in plasmonic tunnel junctions based on indium tin oxide (ITO)/Lu₂O₃/Au. The intensity of SHG is modified over a large range with small applied voltages (<2V) within the tunneling regime. Due to the compact size and unique electrical properties of this approach, this phenomenon can further be employed to realize promising applications including integrated light sources and detectors at the sub-nanometer length scale.